<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="root">
        姓:<input type="text" v-model="firstname"> <br><br>
        名:<input type="text" v-model="lastname"><br><br>
        姓名:<span>{{fullname()}}</span>  
    </div>
    <script src="../vue.js"></script>
    <script>
        Vue.config.productionTip = false
        new Vue({
            el:"#root",
            data:
            {
                firstname:'张',
                lastname:'三'
            },methods:
            {
                fullname(){
                    return this.firstname+this.lastname
                }
            }
        })
    </script>
</body>

</html>